It depends on the ship’s location and the prevailing conditions.
IMO Guidance for Masters on Keeping a Safe Anchor Watch (STCW. 7/Circ. 14) advises as follows: “The master of every ship at an unsheltered anchorage, at an open roadstead or any other virtually “at sea ” conditions in accordance with chapter VIII, section A-VIII/2, part 3-1, paragraph 51 of the STCW Code, is bound to ensure that watchkeeping arrangements are adequate for maintaining a safe watch at all times. A deck officer shall at all times maintain responsibility for a safe anchor watch.”